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In this video, we'll learn about
the if else statement.

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Adding An else section to an if statement
is the obvious next step to

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improving control flow in a program.

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Many times, we want to perform
different actions depending on whether

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the condition is true or false.

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Again, the syntax for the if
else statement is very simple.

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We have the same syntax as for the if
section as in a simple if statement.

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But we add the else keyword and
the statement we want to execute

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when the condition is false.

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So in this case, if the
control expression is true

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we execute statement1.

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And if it's false, we
execute statement2.

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Notice the indentation.

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I can't stress enough how important
good indentation and style is.

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By simply looking at the construct,
we can easily see both sections

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because it's indented properly.

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In this slide, you can see example
code and the flow chart that

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visually shows the flow of control.

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The condition num greater
than 10 is evaluated.

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If that's true, we increment num.

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If it's false, we assign 10 to num.

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In both cases, we then continue
execution to the next statement.

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Let's see a few more examples.

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In the first statement, we
check if num is greater than 10.

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If this is true, we display
num is greater than 10.

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If it's false, we display
num is not greater than 10.

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In the second example, we
check if health is less than

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100 and heal player is true.

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If both these conditions
evaluate to true, then we

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assign 100 to the player health.

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Otherwise, we simply
increment the player health.

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Here we could see sample code
along with a flowchart that

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visually shows the flow of control.

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Notice that in this example,
we're using two block statements

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in the if else statement.

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So if num is greater than
10 is true, we execute both

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statements in the block.

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We increment num, and
we display increment.

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If num is not greater than 10, then
we assign 10 to num and display reset.

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Regardless of which block statement
executes, we continue processing.

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Finally, let's see another example
where we group if else if statements.

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In many cases, we can group
if else statements together.

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Here's a common example.

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Suppose I want to display
a student's letter grade

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given their score on an exam.

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In this case, we can check if
their score is greater than 90.

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If it is, we display
an a., and we're done.

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No other conditions will be checked.

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So we continue to the last output
statement and display done.

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Suppose the student scored a 75.

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First, we check to see if
the score is greater than 90.

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It isn't.

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So we go to the next else
if score greater than 80.

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Again it's, not true.

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Then we check score greater than 70.

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Now it's true, so we
display a c, and we're done.

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No other conditions will be
checked, so we continue to the last

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output statement and display done.

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Notice that the last else in
the construct doesn't have

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an if associated with it.

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This is the catch all else statement.

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If none of the previous if statements
is true, then this l statement

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will execute and f is displayed.

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This is a very very common pattern
that's often seen in programming.

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It's efficient since no extra
checks will be performed once

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we know which condition is true.

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We could obviously change the logic
and start with score less than

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60 and work our way up to an a.

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Let's head over to the IDE and
see some examples in live code.

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I'm in the CodeLite IDE.

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I'm in the section 9 workspace
in the if else statement project.

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This one's really really simple.

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The user is going to enter a number,
and we're going to store it in num.

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And we're going to compare
the number to a target.

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In this case, I just
assigned 10 to the target.

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So we'll ask them enter a number, and
I'll compare it to 10 in this case.

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Okay, we get the number from the user.

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And then we've got a
real simple if statement.

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If the number is greater than or
equal to the target, we're just

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going to display this line, and
then we're going to display the

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number they entered is greater
than or equal to the target.

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That's it.

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We're also going to calculate the
difference between the number

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and the target and display the difference.

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So in this case, in this
piece right here this is the

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if statement right there.

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That's the if section.

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That's the true section.

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We're going to say yeah the
number you entered is greater

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than or equal to the target.

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It's so far away from the -- so
much greater than the target.

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That's it.

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Now if the number they enter is
not greater than or equal to the

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target, then the else part fires.

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And in which case we're still going
to print a line, and then we're

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just going to say the number you
entered is less than the target.

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What's the difference between target
and number, and we're going to

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display that difference as well.

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Okay, so really really
straightforward program.

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Let's compile and run this.

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So in this case let's enter a
number and I'll compare it to 10.

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Let's say I enter 10.

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It says 10 is greater than or equal
to 10, which it is and 10 is 0

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greater than 10 because it is 10.

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Perfect.

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So let's run this a couple more times.

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Let's put in 100, and we get 100
is greater than or equal to 10.

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100 is 90 greater than 10.

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Right, and let's put
in let's negative 10.

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In this case, negative
10 is less than 10.

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And negative 10 is 20 less than
10, which is again correct.

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So you can see real simple program
adding an else section to the if

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statement is really, really simple and
actually it's super powerful because

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it gives you you know the ability to
have a binary decision and execute

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code on both sides of that decision.